NATURAL HIBERNATION OF CAPTIVE TESTUDO HORSFIELDII

Julia A. Davenport

Summary.

The natural behavioural instinct of the species Testudo horsfieldii is the excavation of long tunnels when preparing for hibernation. In captivity the species has a reputation for difficulty in settling the animals down in preparation for hibernation, and they often break through the confines of a container. This report investigates a method of hibernation in a group of captive specimens with observation and reasoning behind the method. This has been carried out successfully for two consecutive winters in an environment which endeavours to replicate habitat conditions.

Description of species

Two pairs of T. horsfieldii are housed together in an enclosure throughout the year. One pair of animals has been in the collection for 4 years and a further pair for 10 years. Both pairs were from confiscations by Customs and Excise. The latter pair are considered to be from a different region in their natural habitat because they have an oval carapace shape, whereas the more recent pair are rounded in shape. The regions from which they came have not been confirmed.

Enclosure construction overall

The enclosure is constructed on a concrete base foundation of 15 cm depth onto which stout wooden boards have been placed. The overall size of the enclosure is 214 cm by 132 cm. The height on one side is 40 cm falling to 22 cm on the opposite side to allow for rainfall drainage. The boards are treated annually with a non-poisonous wood preservative stain.

Enclosure construction: summer

Half the enclosure has a glass covered top. The remaining half has an open mesh top. Both halves are removable for access, but are always closed at night to prevent intrusion from predators, for example foxes. The half with the glass top has a plastic box placed beneath for use as sleeping quarters. This area over a period of time has reverted from a loam base to a dry dust substrate and replicates the desert substrate in the natural habitat. The half with the open mesh top allows rainwater through and forms an undulating grassy area which is kept short by regular clipping.

Enclosure construction: winter

The covers on the two halves of the enclosure are replaced with rigid opaque plastic corrugated sheet on a sturdy framework. Rainwater, therefore, does not enter the enclosure once this is in place. Slates are also placed at an angle around the outside base of the enclosure to allow shedding of any rainfall away from the wooden boards.

Husbandry: summer

The tortoises have access to the grassy area and the dry substrate area at all times, and retreat to the dry area if it is raining. A drinking/bathing water tray is positioned in the grassy area and topped up with rainwater which is available ad libitum. The tortoises occasionally urinate and defaecate in the water. This is then cleaned out and replenished with fresh tap water. The diet consists of natural plant material, for example dandelion, sow thistle, various herbs and red clover with occasional fruit. Vitamin supplements are lightly sprinkled on the food once a week. The food is placed on the grassy area to prevent ingestion of substrate, and is replaced daily.

Husbandry: preparation for winter

At the start of September the tortoises show a more selective interest in food, consumption of which slows down and ceases by the start of October. During this period one of two trial tunnels are excavated with the animals appearing again during the daytime. At this time the covers on the enclosure halves are replaced with the plastic corrugated sheets. Food is withheld when no further interest is shown in eating.

Hibernation

By the end of October, the tortoises ‘disappear’ into individually excavated tunnels in the grassy area, leaving a mound of friable earth behind. In previous winters the animals have been dug manually out of their tunnels in order to be placed in cardboard containers for hibernation. These tunnels have been measured at 52 cm in length. At the end of the tunnel the tortoise excavates a chamber which allows it to turn round and position itself at a slight angle with the head position facing upwards. It is presumed that this angle lessens the risk of any moisture intake through the nostrils and also takes pressure off the lungs in hibernation. The tortoise is also in the correct position to excavate its way to the surface in spring and, should any excessive build-up of solidified soil occur, the effort required to emerge is also lessened. In order to prevent any collapse of tunnels or compaction of substrate, walking in the enclosure is strictly prohibited throughout the hibernation period. Access to the enclosure is possible by leaning over the top from all four sides.

From December onwards until the beginning of March, a layer of horticultural fleece for added frost protection is folded and placed to give four layers over the hibernation area. The recommendation of the fleece for use on plants is that it should give added protection down to -5°C, providing it is kept dry. The plastic box used for sleeping quarters is removed.

Climatic conditions in hibernation

The animals are kept in a private collection in the county of Cheshire, U.K. Cheshire is known for a high annual rainfall, but with careful south facing positioning of the enclosure it can receive direct sun for approximately nine hours in summertime and five hours in the shorter winter days. During the daytime when the weather conditions are favourable the corrugated tops are pushed back to allow circulation of air. This is continued throughout the winter, and especially on a crisp frosty or windy day, which emulates a more natural habitat environment. It only remains closed when there is rain. The enclosure therefore remains dry and cold throughout the hibernation period.

Temperature monitoring

Over the period of two winters temperature was monitored with a digital maximum/minimum memory thermometer in increments of 0.1°C plus humidity readout. The thermometer was positioned on the substrate surface throughout the hibernation period and checked daily. At night the temperature readings were between -11°C and 6°C. During the daytime the temperature readings were between 6°C and 17.9°C. On two particularly sunny days in winter 2003-4 the temperature rose to 39°C.

Humidity readings were mostly between 40% - 60%, with the exception of the highest reading of 70% on one occasion. No readings were taken in the tunnel.

Emergence from hibernation

At the beginning of March daily observation of the hibernation area took place. The horticultural fleece was removed to facilitate this. During both winters 2002-3 and 2003-4 emergence of the tortoises occurred over a two-week period, the earliest on March 2nd and the fourth tortoise on March 15th.

Photo: the enclosure showing one emerged tortoise, and another emerging from the hibernation tunnel on the left of the picture.

The tortoises were covered in the loam substrate, which dried on the carapace and plastron and also covered the head and limbs. This was left to dry naturally and fall away. The tortoises had no difficulty in opening their eyes and mouth and ate within 24 to 72 hours of emerging from their tunnels. They also drank copiously during the first two weeks. The plastic sleeping house was returned immediately to the enclosure, but for approximately seven days the tortoises retreated into their tunnels each night and emerged each morning. They also spent much time actively investigating the enclosure. Once they started to occupy the plastic house they no longer used the tunnels, and these quickly filled in on the surface with substrate.

After approximately two weeks, on a warm sunny day, the tortoises were washed in warm water to which a veterinary anti-fungal solution had been added. A general examination of the animals then took place.

NB. For approximately three months the location of the tunnel area can be identified. This is carried out by tapping with the back of the hand producing a hollow sound. After this time the deeper areas of the tunnels collapse and infill.

Testudo horsfieldii breaking through a cardboard hibernation box.

Discussion

This method of hibernation has been carried out in the U.K., where climatic conditions are not comparable to the natural habitat conditions for T. horsfieldii. The stress factor caused to this species in getting them to settle in a traditional container is visually apparent. Some animals will dig their way out of a cardboard container within a few days. This effort also has the disadvantage of consuming valuable energy prior to hibernation. These two factors may contribute to a lowering of the immune system in some tortoises. The method of hibernation suited to Mediterranean species is not necessarily suitable for other hibernating species such as T. horsfieldii.

Concern has been expressed regarding the escape of the tortoises, due to the length of the hibernating tunnel and the possibility of emergence some distance away beyond the outer perimeter of the enclosure. This has not posed any problem so far, as the tortoises always emerge back up the same tunnel and opening from where excavation commenced. It is assumed that instinct prevents them using energy in digging a way out through unknown substrate and territory.

Emerging T. horsfieldii at tunnel entrance, covered in substrate.

Readers should note that the suitability of hibernating tortoises in the way described may depend on the severity of the winter, the type of soil (sandy soil may collapse, whereas clay could easily become waterlogged), and the level of the water table. Provision should be made for making the hibernaculum vermin-proof, for instance by digging in wire mesh all round the sides of the enclosure so that rats cannot tunnel in. This would also prevent the tortoises from digging shallow tunnels with the possibility of emergence on the wrong side of the enclosure.

The method described certainly has many advantages and has been carried out successfully for two consecutive winters at the time of this report. Detailed monitoring of temperature and humidity in the tunnels, plus hibernation weight loss monitoring, warrant further investigation. With careful management of this hibernation method, I consider that it is possible to carry this out satisfactorily in the U.K., with the provisos mentioned above.

Acknowledgement

I would like to express my thanks to Anne Campbell for assisting me with the literature search.